Ok...my english isnt so good. So model details its really an art, but you can learn a lot looking some video tutorials. I dont know what software do you use to model so I am showing some videos that can help a lot and theres lot more at those sites:

http://www.thegnomonworkshop.com/dvds/ijo01.html

http://gnomonology.com/tutorial/343

Just dont give up when you saw that this inst the software that you use, because almost all softwares have the same or similar tools that can do the same thing at all, you just need to know how to use it.

Here a ZBrush tutorial about details:

http://www.digitaltutors.com/store/product.php?productid=3461&cat=91&page=1

PS. Dont forget GeekatPlay free tutorials:

http://www.geekatplay.com/hexagontutorials/weekly.php

Follow me at euQfiz Digital